The SI unit for potential difference is the volt (V).One volt is defined as 1 joule per coulamb (1 V = 1 J C-1).An alternative name for potential difference is voltage.
The potential at a point is numerically equal to the work done in bringing a unit of positive charge from infinity to that point.
A potential difference will appear across a resistor whenever a current flows through it.Electrical energy is converted to thermal energy and in some cases to light.figure 1.23(a) shows the drop in potential along three resistors connected in series.